#include <stdio.h>
int main()
{
    int x;
    scanf("%d", &x);

    if(x < 0 || x > 100)
    {
        printf("输入有误\n");
        return -1;
    }
    switch(x/10)
    {
        case 10:
        case 9:
            printf("A\n");
            break;
        case 8:
            printf("B\n");
            break;
        case 7:
        case 6:
            printf("C\n");
            break;
        default:
            printf("D\n");
    }
}